The problem: Combining multiple PDF files into a single file, so you don't inflict a half-dozen PDF files on the accounting department when you know they'll lose track of more than one file. Or maybe you have four or five sections of a report that you've printed to separate PDF files from Word, Excel, and a photo editor. How do you get them all into a single PDF?

If you use a Mac, you have the only tool you'll need already built into the macOS operating system, though you can find more flexible and full-features solutions if you buy commercial third-party apps. If you use Windows, you'll need third-party apps, but you can find free open-source apps that do the job. There are also online apps that offer to combine and edit PDFs that you upload, but I don't recommend any of them. Your PDF files contain invisible metadata, potentially identifying you and your system, and you may not want to give that metadata to a website that offers free editing features. That site may want to profit from your data in ways you won't like.

How to Combine PDFs in Windows

When you need to combine PDF files in Windows, you may decide that you wish you had a Mac, where the Preview app gets the job done quickly and easily. Windows 10 lets you view PDF files in the Edge browser, but doesn't let you do anything with them. To merge or manage PDF files, you'll need either a free but limited third-party productivity app or one of a variety of well-designed commercial apps.

If your PDF-managing needs are minimal, install the free PDFsam from www.PDFsam.org. If you want the free product, uncheck the option in the installer to download the Enhanced version, which is free to preview but $49 to keep. A spacious interface lets you choose among functions like merging and splitting PDFs files, plus a nifty feature that combines two PDF documents, alternating the pages from one file with the pages from the other, so you can create a single PDF from separate PDFs that contain the front and back pages of an original two-sided document.

Don't expect an easy-to-use interface like the thumbnail views in Adobe Reader and other commercial software. You merge two PDF files by dragging them into a PDFsam window, which adds them to a list. You can specify a page range from each PDF, but you'll have to figure out which pages you want by viewing the document in a separate app like Microsoft Edge or Adobe Reader. Fortunately, you can open PDFs directly from the file list in PDFsam. When you're ready to merge the PDFs, click the Run button and a merged PDF gets created.

If you want better visual cues when merging PDFs, you'll need a commercial app that lets you see the combined PDF before you save it to disk and also displays thumbnail images that you can drag up and down in a sidebar in order to rearrange the pages. You can use almost any PDF-editing software, ranging from the moderately priced PDF-Xchange Editor from Tracker Software, or choose one of our Editor's Choice apps like ABBYY FineReader 14 or Adobe Acrobat DC.

All these apps let you combine PDFs in basically the same way. Here's how PDF-XChange Editor does it. The simplest method is to use File->New Document, and choose the option to Combine Files into a Single PDF. A file-list box will open. Drag into it the files that you want to combine into a single PDF. You can add PDF files, or any combination of text, Word, Excel, or PowerPoint documents into the list, and the app will convert them into PDF format while combining all the files into a single PDF.

When combining files, you can specify the page range that you want to import, but you can also fine tune the combination by opening multiple files in separate tabs in PDF-XChange Editor and dragging thumbnail images of the page you want from the source tab to the target tab (if thumbnails aren't visible, press Ctrl-T or use the View > Panes menu).

How to Combine PDFs on a Mac

Unlike Windows, macOS comes with high-powered PDF tools built in—provided by the deceptively modest-looking Preview app. To combine two or more PDF files in Preview, start by making a copy of one of the files and working with the duplicate (this is an essential precaution because Preview saves the file as you work, and if the results aren't what you want, you'll need to do some fancy footwork to get back the original file).

Open the duplicate file. If thumbnails aren't visible in Preview's sidebar, go to the View menu to switch them on. Next, simply drag additional PDF files into the sidebar and drop them at the position in the file where you want them to be—at the start or end, or between any two existing pages. If you get the location wrong, you can drag one or more thumbnails to the correct location, and you can delete any pages that you don't want.

What if you only want to merge a few pages from a second PDF file? Open that file in another PDF window and drag the thumbnails that you want into your first PDF file. As always in macOS, you can Shift-click to select a continuous range of pages, or Cmd-click on multiple pages to select pages from anywhere in the file. If some pages get imported in the wrong orientation, use Preview's toolbar to rotate them.

Sometimes Preview acts in seemingly unpredictable ways when saving a file, so, when you have the combined pages arranged as you want them, choose File > Export to PDF and save the merged PDF under its own name. You can also choose File > Close, and follow the prompts to save the merged file under the name of the file you started with, but it's safest to use the Export to PDF option.

Preview has another PDF-merging trick that isn't immediately obvious. You can merge any file that Preview can display into an existing PDF. That means you can drag any PNG, TIFF, JPEG, or other standard image format into a PDF. But what if you want to create a PDF that contains a Word document or an Excel worksheet? You can't drag those documents into Preview, but you can use the Print menu in Word or Excel to create PDF files that you can use for a merge.

Alternatively, if you have a third-party app like Adobe Acrobat, you can merge PDFs in the same way that you merge them in Preview—but you can also directly drag files in any file format that Acrobat knows how to convert into PDF, including HTML web pages, plain text files, Word documents, and Excel worksheets. Acrobat also lets you create a completely new PDF from one or more of these same external formats. Simply use the File > Create menu and follow the prompts.

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